Supply reel



y 17, 1955 E. N. DINGLEY, JR

MAGNETIC TAPE RECORDER-REPRODUCER Original Filed Aug. 16, 1951 TA KE-UP REEL TAKE-UP REEL AuPLiF/m :o umvasa 7 am PASS nonuu ran mrsn um I l x A mum amp PASS OSGILLATO; mrzn ran 0 or rare. moan: POWER I i 26 SOURCE saunuzsn Pnosmu mausouazn FIG 2 Inventor UnitedStates Patent Oflice Re. 24,182 Reissued July MAGNETIC TAPE RECORDER-PRODUCER I Edward N. Dlngley, In, Arlington, Va.

Original No. 2,656,419, dated October 20, 1953,, Serial No. 242,117, August 16, 1951. Application for reissue December 1, 1954, Serial No. 472,546

15 Claims. (Cl- 179-1003) 3 My invention relates broadly to equipment utilizing a magnetizablc tape or wire as a storage medium for recordmg and reproducing complex electrical signals which are hereinafter called The Program."

My invention relates chiefly to circuit arrangements and mechanical structures whereby undesirable effects arising from variations of the linear velocity of the storage medium (hereinafter called "tape") are eliminated or greatly reduced.

One object of my invention is to eliminate or greatly reduce the undesirable efiect in the reproduced program which is termed flutter or wow" by those skilled in the art.

Another object of my invention is to eliminate the difference betweenthe average speed of the tape during recording and the average speed of the tape during reproduction in order that the program will be reproduced in the same time interval as was required during recording.

Another object of my invention is to provide means whereby the recorder may be synchronized to a motionpicture camera and means whereby the reproducer may be synchronized to a motion-picture projector whereby the program recorded during the photographing of an action will be reproduced in synchronism with the projection of the action.

Other and further objects of my invention will be understood from the following specification and by reference to the accompanying drawings in which:

Figure 1 schematically represents the recording equipment.

Figure 2 schematically represents the reproducing equip ment.

Since this invention pertains chiefly to the transport system for controlling the velocity of the tape, I have omitted hereirom any description of the adjuncts to magnetic recorders such as provision for bias and erasure and other details well known to those skilled in the art but which have no bearing on this invention.

In Figure 1, the essentials of the tape transport system of magnetic recorders well known to the art are portrayed by: The supply reel 101 and the take-up reel 102 which may be driven by separate servo systems (not shown) to preserve constant tension in the tape 111; the tape drive motor 103 which drives the tape by means of the capstan 104 and the pressure idler 105; and the record-head 107 which is energized through the amplifier 109 from the program source 110. The synchronous capstan motor 103 is energized from a source 106 of A.-C. power. The portion of my invention which applies to the recorder consists of the addition of the timing oscillator 108, the output of which (having frequency f) is amplified by amplifier 109 anti applied to the record-head 107 together with the signal from the program source 110. The major portion of my invention, as described hereinafter, concerns the utilization 5 reel 1 and thetake-up reel 2 which are'pref erably driven by separate servo systems (not shown) to preserve constant tension in the tape 6; the tape drive motor 5 which drives the tape by means of the capstan 3 and the pressure idlerl; and the reproduce head 7 which is mounted in the guide racks 8 and which is capable of linear motion parallel to the travel of tape 6 under the influence of force exerted by the solenoid 9.

In Figure 2, the drive motor S'may be a D.-C. motor or a series ArC. motor, the speed of which is controlled by the manually operated rheostat 11, and by the vernier 'rheostat 12 which is positioned by the reversible motor 13 through the means of worm 14 and gear 15. The motor 13 is caused to rotate in a forward direction by the closure of spring contacts 16 and 18, and in a reverse direction by the closure of spring contacts 16 and 17.

The mode of operation of the magnetic reproducer equipment is as follows: During the starting operation, the magnetic tape 6 is accelerated by applying power to the capstan motor 5. As thetape 6 approaches normal velocity, the timing signal which was derived from oscillator 108 (Fig. l) and recorder on the magnetic tape, will be reproduced by the reproduce head-7, amplified by the amplifier 10 and passed by the band-pass filter 20 when its frequency has increased to within 1% of frequency f, whereupon this timing signal (hereafter called i) will be mixed in the balanced modulator 21 with a signal of frequency 15 derived from the timing oscillator 22. The resultant diflerence-frequency which appears at the output terminals A of the balanced modulator 21, is applied to the armature 9 of a solenoid which is provided with a permanent magnetic field designated as N and S in Figure 2. The armature 9 is rigidly connected 1 to the reproduce-head 7 by means of the mechanical linkage 24.

The difference frequency applied to armature 9 causes said armature to start to vibrate, but the direction of motion of said armature during the first (or third) quartercycle of its vibratory motion is such as to move the reproduce-head 7 in a direction opposite to the motion of the tape- 8. The resultant increase in the velocity of the tape 6 relative to the velocity of the reproduce-head 7 is such as to reduce the ditfercnce-frequency to nearly zero, or, stated in another way, such as to produce a phase difierence betweenf' and f of some value between (for which value the armature is not energized) and for which value the armature 9 receives maximum value of direct current). The phase difl'erence t will tend to increase because, at the moment under consideration, the velocity of tape 6 is less than normal. As the phase difference tends to increase, the direct current in armature 9 also tends to increase, thus moving the reproduce head 7 further in a' direction opposite to that of the tape motion and this motion tends to decrease the phase difference 4:. The phase difierence p at any instant will be that phase diflerence which produces sutncient direct current in armature 9 to hold the reproduce-head 7 in the proper position displaced from a normal position to which it tends to return through the action of suspension springs not shown.

A rigid mechanical linkage 26 connects the" reproduce head 7 to contact spring 16. In consequence, the above described motion of the said reproduce-headcauses spring 16 to make contact with spring 18, thus causing motor 13 to revolve in such a direction as to reduce the resistance of rheostat 12, thus causing an increase in the speed of capstan motor 5 and a consequent increase in the to increase thus reducing the phase-difference 4, thus re- 7 ducing the current in armature 9, and thus permitting the reproduce-head 7 to return progressively toward its normal position through the action of its suspension springs not shown. When the reproduce-head 7 assumes its normal position, spring 16 is disengaged from spring 18, the motor 13 ceases to rotate and the average speed of capstan motor 5 and tape 6 remains approximately constant. Should the average speed of tape 6 be greater than normal, the average position of reproduce-head 7 will be off normal in the direction of tape motion, contacts 16 and 17 will close, and motor 13 will adjust rheostat 12 so as to reduce the average tape speed until contacts 16 and 17 are opened. Any short term variations, flutter or wow, which tend to appear in the frequency f due to irregularities in the tape velocity either during recording or reproduction, will tend to advance or retard the phase difference in proportion to the instantaneous time-position error of the signal storage medium relative to the reproduce-head 7. This immediately results in motion of the reproduce-head 7 in such a direction as to reduce the time-position error and the resulting phase difference to a minimum. In consequence, the variation of phase difference p is held to a minimum. In further consequence, the rate-of-change (de/dt) of the phase difference p is held to a Since do/dt represents the instantaneous frequency difference between f and f, it follows that this frequency difference (flutter or wow) is held to a minimum. Since the frequency f and the various frequencies constituting the program are derived from the same magnetic tape, it follows that the flutter and wow in the reproduced program is held to a minimum. The reproduced program passes through the band-pass filter 25, which attenuates frequency f, through the usual equalizer 26 and to the transducer or loudspeaker 27.

The technical literature contains descriptions of types of magnetic media recording-reproducing equipment which utilize the principle of recording atiming signal simultaneously with the recording of the program and which utilize the reproduced timing signal to apply instantaneous speed corrections to the capstan motor of the reprodueer in an endeavor to maintain the correct media velocity from instant to instant. Although these types of equipment are capable of maintaining the correct average velocity of the media, they are incapable of reducing materially the short period variations in the instantaneous velocity of the media because of the excessive inertia of the rotor of the capstan motor. My in vention not only maintains the correct average velocity of the media but also materially reduces the short period variations (flutter and wow) by providing a reproducehead having small inertia and having the ability to move automatically parallel to the media in such a manner as to greatly reduce the effect of short period variations in the instantaneous velocity of the magnetic media.

Oscillator 108 of Figure 1 and oscillator 22 of Figure 2 may be highly stable oscillators having substantially identical average frequencies and having negligible short term frequency variations. Under these circumstances the maximum variation of the frequency f and the maximum flutter and wow of the program will not exceed the sum of the negligible short term variations of the two oscillators plus the maximum rate of change dldt of the phase difference p. The later rate of change will be proportional to the difference between the time intergral of the inadvertent accelerations of the tape, during recording and reproduction, and the time integral of the acceleration of the reproduce head 7 resulting from the force applied by the solenoid 9. Since the acceleration of the reproduce head is proportional to the applied force and inversely proportional to the mass of the head, it follows that the acceleration requiredto maintain negligibly small values of do/dt can be attained by means of a reasonably small force provided that the mass of the reproduce head is also small. Since o is not permitted to vary by more than 1 radians, the time required to reproduce the program will not differ from the time required to record the program by substantially more than 1/2 f seconds.

The frequency f of oscillator 108 of Figure 1 and of oscillator 22 of Figure 2 may be any desired frequency within the response capability of the equipment. It would be undesirable to select a frequency f within the band of frequencies occupied by the program but such a frequency could be accommodated by obvious methods such as by providingvadditional filters or a separate timing track on the tape.

There is a certain advantage in selecting C. P. S. as the frequency f because it is less than the lowest frequency required for the reproducedprogram, because the 60 C. P. S. synchronous motor of a motion-picture camera can be energized from oscillator 108 and because the 60 C. P. S. synchronous motor of a motion-picture projector can be energized from the oscillator 22, thus assuring not only a very low flutter and wow in the reproduced program but also assuring the maintenance of exact synchronism between the audio program and the projected motion-picture action. It is possible to achieve the required synchronism by substituting the commercial 60 C. P. S. mains for oscillators 108 and 22 but in this case the percent wow and flutter is still equal to the sum of the percent short term frequency variations of sources 108 and 22 which, in the case of power mains, may be appreciable. The exact synchronism between the reproduced audio program and the projected motionpicture would be maintained because the synchronous motor of the projector is energized from the source 22. Should the average frequency of the source 22 be 1% higher than the average frequency of source 108, then the motion picture would be projected with 1% higher film speed and the audio program would be reproduced with all frequency components thereof increased by 1%. but these conditions would not materially degrade the quality of the program or the picture.

There is a certain advantage in choosing the frequency f of sources 108 and 22 to be greater than the highest frequency required for the program, say, 15 kc. TlllS advantage lies in the fact that the resulting wavelength of the timing signal on the tape will be shorter than for a 60 C. P. S. timing signal. In consequence, a specified linear time-position error of the tape will result in a larger value of p, which will produce a larger correction current in solenoid 9, which latter phenomena will result in a .stiffer" or more accurate correction of flutter and wow. The disadvantage of choosing the frequency f of oscillators 108 and 22 to be 15 kc. is that additional circuitry of a kind well known in the art, will be required to synchronize the synchronous 60 C. P. S. motors of the motion-picture camera and projector to the 250th subharmonic of the 15 kc. signal produced by oscillators 22 and 108.

In Figure l the A.-C. power source 106, which drives the capstan motor 103 of the recorder, may be the 60 cycle mains since variations, within reasonable limits, in the average and instantaneous speed of this motor, which would otherwise produce flutter or wow in the reproduced program, are eliminated or greatly reduced by the automatically controlled motion of the reproduce head of the reproducer.

In Figure 2 the latitude of motion of the reproducehead 7 along its guides 8 should be suflicient to tolerate the maximum linear time-position error of the tape which is likely to occur due to time delays resulting from inertia in the rotors of motors S and 13. This maximum timeposition error usually will not exceed plus or minus 0.1 inch.

It is preferable that the signals of frequency f generated by timing oscillators 108 and 22 be approximately sinusdidalzbut other wave shapes may be utilized if desired. The balanced demodulator .21 and the solenoid 9 maybe replacedby any of several combinations of devices, well to the art, which will impart to. reproduce-head 7, a motion which is substantially proportional to the phase difference p, or to the time-displacement existing between f and f of Figure 2. a In Figure 2 the combination of the spring contacts l6, l7 and 18, the motor 13, the gears 14, 15, and the rheostat 12, comprises only one simple method of controlling the average speed of motor 5 and is portrayed to illustrate the principle of operation. There are several servo-control systems, well known to the art but unnecessarily complex for illustration herein, whereby the average speed of motor 5 may be increased or decreased in proportion to the linear displacement of the reproducehead 7 from its, normal center position.

In Figure 2 the straight-line mechanical linkages 24 'and 26 are depicted solely for illustrative purposes.

There are many mechanical linkage systems well known to those skilled in mechanical design which would serve to impart the motion of the electro-mechanical transducer (illustrated in Fig. 2 by solenoid 9) to the reproducehead 7 and to the servo-control which is illustrated in Figure 2 by the contacts 16, 17, and 18. For example, it is sometimes desirable to impart rotary motion instead of linear motion to the reproduce-head 7 in order to control the instantaneous time position of the head 7 relative to the tape 6.

In Figure 2 the band-pass filters and may com-. prise any devices, well known to those skilled in the art, which are capable of etfectively separating the reproduced timing signal from-the reproduced program.

In certain applications it is desirable to reproduce the program at a rate different from the rate at which it was recorded. In practicing my invention, this may be accomplished by adjusting the average frequency of oscillator 22 to be diflerent from thatof oscillator 108.

If desired, a synchronous motor similar to motor 103 of Figure 1 may be mounted on the same shaft as motor 5 of Figure 2 and other similar adaptations may be made whereby the recording and reproducing functions may be accomplished by one equipment or assemblage.

What is claimed is:

1. A signal recording and reproducing apparatus comprising means for recording a complex electrical signal and a timing signal on a moving signal storage medium, moveable signal-reproducing means for reproducing the recorded complex electrical signal and the recorded timing signal, means for separating said reproduced signals,

and means for utilizing the phase variations of the reproduced timing signal to position the said moveable signal-reproducing means including means to correct the average speed of the said moving signal-storage medium in such manner as to reduce or eliminate frequency variations in the said reproduced timing signal and to reduce or eliminate flutter and wow in the reproduced complex electrical signal.

. 2. A signal recording and reproducing apparatus comprising means for recording a complex electrical signal and a first timing signal on a moving signal storage medium, moveable signal-reproducing means for reproducing the recorded complex electrical signal and the first said timing signal, means for separating said reproduced signals, means for generating a control signal of magnitude proportional to a function of the phase difierence between the reproduced first timing signal and a second timing signal, means responsive to said control signal for positioning said moveable signal-reproducing means to maintain a minimum phase-difierence between the said reproduced first timing signal and the said second timing signal, and means responsive to a positioning other than normal of the moveable signal-reproducing means for adjusting the average speed of the moving signal storage medium program together with a first timing signal to which the motion of the film being exposed is synchronized, moveable signal-reproducing means for reproducing the recorded complex electrical signal and the said first timing signal, means for separating said reproduced signals, means for generating a control signal of magnitude proportional to a function of the phase difierence between the reproduced first timing signal and a second timing signal, means responsive to said control signal for positioning said moveable signal-reproducing means to maintain a minimum phase-difference between the said reproduced first timing signal and the said second timing signal, means responsive to a position other than normal of the moveable signal-reproducing means for adjusting the average speed of the moving signal-storage medium in such manner as to cause the moveable signal-reproducing means to resume its normal position, and means for synchronizing the motion of the film during projection with the frequency of the saidsecond timing signal.

4. The apparatus of claim 3 wherein a motion-picture camera is synchronized to the first timing signal and wherein a motion-picture projector is synchronized to the second timing signal.

5. The apparatus of claim 3 wherein the moving signalstorage medium comprises a magnetizable tape or wire.

6. The apparatus of claim 3 wherein the moveable signal-reproducing'means comprises a light-weight mag netic reproduce-head capable of motion substantially parallel to the direction of travel of the moving signalstorage medium.

7. The apparatus of claim 3 wherein the control signal of magnitude proportional to a function of the phasedifference between the reproduced first timing signal and the second timing signal is derived from the output of a modulator having applied to its input terminals the reproduced first timing signal and the second timing signal.

8. The apparatus of claim 3 wherein the means responsive to said control signal for positioning said moveable signal-reproducing means comprises a solenoid arranged to impart to the moveable signal-reproducing means a displacement from normal proportional to the magnitude of said control signal in a direction parallel to the direction of, travel of the moving signal-storage medium.

9. The apparatus of claim 3 wherein the means responsive to a positioning other than normal of the moveable signal-reproducing means for adjusting the average speed of the moving signal-storage medium comprises a moveable contact spring afiixed to the said moveable signal-reproducing means which makes contact with one of two fixed contact springs whenever the said moveable signal-reproducing means is positioned in other than its normal or center position, a motor whose direction of rotation is determined by which of the two said fixed contact springs makes contact with said moveable contact spring, and gears by means of which said motor rotates a rheostat for controlling the power delivered to the capstan motor which drives the said moving signalstorage medium.

10. A signal recording and reproducing apparatus comprising means for recording a complex electrical signal and a timing signal on a moving signal storage medium, moveable signal-reproducing means for reproducing the recorded complex electrical signal and the recorded timing signal, means for separating the reproduced signals, and means operatively associated with the signal reproducing means for utilizing phase variations of the reproduced QQIBB tinting signal to position the moveable signal-reproducing means.

II. A signal recording and reproducing apparatus comprising means for recording a complex electrical signal and a first timing signal on a moving signal storage medium, moveable signal-reproducing means for reproducing the recorded complex electrical signal and the recorded first timing signal, means for separating the reproduced signals, means operatively-associated with the signal reproducing means for generating a control signal of magnitude proportional to a function of the phase diflerence between the reproduced first timing signal and a second timing signal, and means responsive to said control signal for positioning the moveable signal-reproducing means to maintain a predetermined phase relationship between the reproduced first timing signal and the second timing signal.

12. A signal recording and reproducing apparatus comprising means for recording a complex electrical signal and a timing signal on a moving signal storage medium, moveable signal-reproducing means for reproducing the recorded complex electrical signal and the recorded timing signal, means for separating the reproduced signals, means operatively associated with the signal reproducing means for utilizing the phase variations of the reproduced timing signal to import to the moveable signal reproducing means a motion which is a function of the phase relationship between the reproduced timing signal and a second timing signal to reduce or eliminate the short period flutter of the reproduced timing signal and of the reproduced complex electrical signal,

and means connected to the moveable signal reproducing reproduced signals, and means operatively associated with the signal reproducing means for utilizingfthe phase means for reproducing the recorded complex electrical signal and the first timing signal, means for separating the reproduced signals, means for generating a control signal of magnitude proportional to a function of the phase difierence between the reproduced first timing signal and a second timing signal, and means operatively associated with the signal reproducing means responsive to said control signal for positioning the moveable signalreproducing means to maintain a predetermined phase relationship between the reproduced first timing signal and the second timing signal.

15. 'A signal reproducing apparatus for reproducing signals from a moving signal storage medium on which a complex electrical signal and a first timing signal have been recorded, comprising moveable signal-reproducing means for reproducing the recorded complex electrical signal and the first timing signal, means for separating the reproduced signals, means operative! associated with the signal-reproducing means for utilizing the phase variations of the reproduced first tinting-signal to impart to the said moveable signal-reproducing means a motion which is a function of the phase relationship between said reproduced first timing signal and a second timing signal to reduce or eliminate the short period flutter of said reproduced first timing signal and of said reproduced complex electrical signal, and an instrumentality connected to the moveable signal reproducing means and responsive to a positioning other than normal of the moveable signal-reproducing for adjusting the average speed of the moving signal storage medium to cause the moveable signal-reproducing means to resume its normal position.

No references cited. 

